Strain-wave / harmonic reducers

A reduction stage used to trade motor speed for output torque. The complete joint also depends on its motor, bearings, sensing and control.

Inside a strain-wave reducer

Inspect the toothed cup, fixed ring, elliptical cam and thin-raced bearing. Turn the input to see how a two-tooth difference creates slow output rotation.

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Three-part reduction

The wave generator deforms the cup. A difference in tooth count produces slow output rotation opposite the input.

Output angle
0
Reduction ratio
50:1

100 flexspline teeth · 102 ring teeth. One input turn moves the output 7.2° in the opposite direction.

About this model

Original Korthos illustrative geometry, not a manufacturer’s product or manufacturing CAD. Ideal 100/102-tooth example with the circular spline fixed: 50:1 reduction in the opposite direction. Detailed cup surfaces, a bearing, mounting holes and reference marks are original illustrations. Tooth profiles, ovalisation, rolling-element motion and the highlighted engagement regions are schematic, not validated contact geometry. No load, stress or backlash simulation. Operating principle.

Model scope & reuse
Architecture, materials & specificationsArchitecture options, material requirements and integration constraints

Architecture options

These are packaging and integration choices within strain-wave gearing; they use the same operating principle.

ApproachMechanismAdvantagesTrade-offs
Cup-style flexsplineA thin toothed cup flexes inside a rigid ring.The cup provides a path from the flexible teeth to the output connection.Cup length constrains packaging; repeated bending contributes to fatigue loading.
Hat-style flexsplineA flanged flexible member changes the mounting arrangement.Offers a different axial package and attachment geometry.The series defines the mounting geometry, fits and ratings.
Component setThe builder integrates the gear elements into its own assembly.More freedom over the housing and bearing arrangement.The builder is responsible for support, alignment, assembly and lubrication.
Complete gear unitThe housing and supporting components are supplied as an assembly.Reduces the mechanical integration work.The supplied dimensions and bearing arrangement constrain the joint design.

Specifications & operating limits

A 100:1 ratio means 100 input revolutions for one output revolution in the specified arrangement. Torque rises with reduction, allowing for losses. Backlash is clearance between mating teeth; lost motion on reversal can also include elastic deformation. Torsional stiffness describes resistance to twisting under load.

Materials & constraints

Fatigue-resistant gear steel
The thin flexible gear bends on every input revolution while its teeth transmit load. Heat treatment, tooth-root geometry and surface condition affect bending fatigue and tooth wear.
Bearing steels & rolling elements
The wave-generator bearing supports the changing shape of the flexible gear. Contact stress, fit and lubrication affect both friction and service life. An output bearing may be separate or integrated.
Grease & seals
Lubricant must remain effective across the intended temperature, speed and load cycle. Grease choice and quantity affect friction and heating; a nominally low-backlash reducer can still deform elastically under load.

Dependencies & engineering limits

Precision manufacturing & repeatability
The flexspline, rigid ring and wave generator need accurate geometry as well as controlled alignment. Repeatable accuracy and life across a production batch depend on the process as well as the design.
Support & output accuracy
The surrounding bearings and housing carry loads and maintain alignment. Housing and mounting deflection contribute to output error alongside gear backlash.
Bearings
Lubrication & service
Lubricant type, quantity and replacement interval are model-specific. The teeth, wave-generator bearing and flexspline interfaces need lubrication; a sealed unit still has model-specific service limits.
Reduction & speed & loading
Greater reduction lowers output speed for a given motor speed. Rated, repeated-peak and emergency torque describe sustained, cyclic and exceptional loading.
Frameless motors

Manufacturing & assembly

Guide

About this route

The route shows one process or architecture. Select a step to see its function and connections; related parts can be parallel inputs or alternatives.

Function

Inputs & dependencies
Outputs & connections
Related processes & parts
Sources

Manufacturing · Representative route. Machined elements become a matched reduction stage for a rotary joint.

Related parts & processes 5

Precision machining

Equipment-maker reference · Gleason

Gear teeth and locating surfaces require controlled geometry. Machining and inspection capabilities determine the fit of the mating parts.

The gear design determines the machining and metrology requirements.

Equipment for this step →
Sources & technical scope

Illustrative images of generic materials and components.

Related references
Link to this detail

Production equipment

Market context

Unitree · planetary joint production

Unitree’s integrated joints combine permanent-magnet motors with planetary reducers designed for leg-impact loads. The filing describes this technology as being in mass production.